Metal to metal packoff for use in a wellhead assembly

ABSTRACT

A wellhead assembly having an inner tubular insertable into an outer tubular. A packoff is provided on an outer surface of the inner tubular for sealing between the inner and outer tubulars. The packoff includes an energizing ring, a U-shaped seal member, and a nut for retaining the seal member against the energizing ring. The seal member includes legs that are spaced apart by interaction with the energizing ring. The outer tubular has a bore wall that is profiled so that when the inner tubular is inserted into the outer tubular, an outer leg of the seal member is spaced radially outward from the bore wall until the inner tubular is landed in the outer tubular. When the inner tubular member is landed, a portion of the bore wall adjacent the outer leg tapers radially inward into sealing contact with the outer leg of the seal member.

BACKGROUND

1. Field of Invention

The invention relates generally to wellhead assemblies and in particularto a system and method for sealing between tubulars in a wellheadassembly.

2. Description of Prior Art

Wellheads used in the production of hydrocarbons extracted fromsubterranean formations typically comprise a wellhead assembly attachedat the upper end of a wellbore formed into a hydrocarbon producingformation. Wellhead assemblies usually provide support hangers forsuspending production tubing and casing into the wellbore. The casinglines the wellbore, thereby isolating the wellbore from the surroundingformation. The tubing typically lies concentric within the casing andprovides a conduit therein for producing the hydrocarbons entrainedwithin the formation.

Wellhead assemblies also typically include a wellhead housing adjacentwhere the casing and tubing enter the wellbore, and a production treeatop the wellhead housing. The production tree is commonly used tocontrol and distribute the fluids produced from the wellbore andselectively provide fluid communication or access to the tubing, casing,and/or annuluses between the tubing and casing. Valves assemblies aretypically provided within wellhead production trees for controllingfluid flow across a wellhead, such as production flow from the boreholeor circulating fluid flow in and out of a wellhead.

Seals are used between inner and outer wellhead tubular members tocontain internal well pressure. The inner wellhead member may be atubing hanger that supports a string of tubing extending into the wellfor the flow of production fluid. The tubing hanger lands in an outerwellhead member, which may be a wellhead housing, a production tree, ora tubing head. A packoff or seal seals between the tubing hanger and theouter wellhead member. Alternately, the inner wellhead member might hean isolation sleeve secured to a production tree. A seal or packoffseals between the isolation sleeve and a casing hanger located withinthe wellhead housing.

SUMMARY OF THE INVENTION

Provided herein is an example of a wellhead assembly that includes anouter tubular having a bore that defines a bore wall, an inner tubularinsertable into the bore and selectively set in a landed position in thebore, a packoff on the inner tubular, and a taper strategically locatedthe bore. When the inner tubular is inserted into the bore, the packoffis in sealing contact with the bore wall when the inner tubular isproximate the landed position, and the packoff is set radially inwardfrom the bore wall when the inner tubular is above a location proximatethe landed position. In an embodiment, the packoff includes anenergizing ring with a protrusion, a seal element having spaced apartlegs that terminate on opposing sides of the protrusion, and a retainingnut threaded to the inner tubular and on a side of the seal elementdistal from the energizing ring. In this example, the seal elements agenerally annular member. One of the legs can be spaced radially outwardfrom the protrusion when the when the inner tubular is above a locationproximate the landed position. Further, one of the legs may be wedgedbetween the taper and the protrusion when the when the inner tubular isproximate the landed position. In one example embodiment, one of thelegs projects radially outward to define a seal between the outertubular and the seal element and another one of the legs projectsradially inward to define a seal between the inner tubular and sealelement. Optionally, the inner tubular is a tubing hanger and the outertubular is a tithing head. Alternatively, the bore wall projectsradially inward at an axial location below the taper to define ashoulder on which the inner tubular lands.

Another example of a wellhead assembly is provided herein that includesan outer tubular having an axial bore, a taper formed in the bore wherea surface of the bore projects radially inward, a shoulder formed in thebore below the taper, an inner tubular landed on the shoulder, and apackoff. In this example the packoff has an outer radius in sealingcontact with the taper and that is set radially inward from a portion ofthe bore between the taper and an upper end of the bore. An inner radiusof the packoff is in sealing contact with the inner tubular. In oneexample, the packoff includes an energizing ring, a seal element withlegs spaced apart by the energizing ring, and a retaining nut for urgingthe seal element against the energizing ring, and beads on the legs thatform a seal against the inner and outer tubulars. Optionally the sealelement can be metal. The energizing ring can also include a protrusionon which the legs are supported. In an example, the inner tubular is atubing hanger and the outer tubular is a tubing head.

Further disclosed herein is a method of sealing between tubulars in awellhead assembly. One embodiment of the method includes providing aninner tubular having a packoff circumscribing a portion of the innertubular, providing an outer tubular having a bore with a taper so that aportion of the bore above the taper has a radius greater than a radiusof the packoff, and a portion of the bore below the taper has a radiusless than the packoff, and sealing between the packoff and the bore byinserting the inner tubular into the outer tubular at least to a depththat the packoff contacts the portion of the bore having a radius lessthan the packoff. The method can further include landing the innertubular in the outer tubular. In this example, the packoff includes anenergizing ring with a protrusion, a seal element having spaced apartlegs that terminate on opposing sides of the protrusion, a soft metalcoating on the seal element, and a retaining nut threaded to the innertubular and on a side of the seal element distal from the energizingring.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side sectional view of an example of a portion of a tubinghanger having a packoff in accordance with the present invention.

FIG. 2 is a side sectional view of the tubing hanger of FIG. 1 landingin a tubing head in accordance with the present invention.

FIG. 3 is a side sectional view of the tubing hanger landed in thetubing head of FIG. 2 in accordance with the present invention.

FIG. 4 is a side partial sectional view of an example embodiment of thetubing hanger of FIG. 1 set in a wellhead assembly in accordance withthe present invention.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.Accordingly, the improvements herein described are therefore to belimited only by the scope of the appended claims.

An example embodiment of a tubing hanger 10 is shown in side sectionalview in FIG. 1, wherein the tubing hanger 10 includes a packoff assembly12. In the example of FIG. 1, the packoff assembly 12 is made up of anenergizing ring 14 that is a generally annular member and having a base16 with a substantially rectangular cross-section. Depending downwardfrom the base 16 is a lower member 18 that in the example of FIG. 1 hasa width less than the width of the base 16 and tapers axially inwardwith distance away from the base 16. The lower member 18 defines aprotrusion that extends into a seal element 20 shown disposed on anouter surface of the tubing hanger 10 and just below the energizing ring14. The seal element 20, which is a generally U-shaped member, has abase 22 which is generally rectangular in cross-section and a pair oflegs 24 that project upward and on opposing lateral sides of the lowermember 18. Optionally, the leg 24 shown facing outward from an axisA_(X) of the tubing hanger 10 is spaced apart from the energizing ring14 to define a gap 25 between the leg 24 and energizing ring 14.Additionally, the spaced apart legs 24 define a space 26. On opposingouter surfaces of the legs 24 are beads 28 that are raised portions onthe inner and outer radial surfaces of the seal element 20 and as willbe described in more detail below, enhanced formation of a sealingsurface between the seal element 20 and another solid member. A group 30is provided on the outer circumference of the tubing hanger 10 in whichthe energizing ring 16 and seal element 20 is disposed. A lower groove32 also on the outer surface of the tubing hanger 10 extends downwardfrom a lower end of the upper groove 30 and as shown in FIG. 1 has areduced radius over that of the upper groove 30. Threads 34 extend alongthe face of the lower groove 32 and provide connection between thetubing hanger 10 and a retaining nut 36 shown threaded into placedwithin the lower groove 32. In one example embodiment, the retaining nut36 provides axial support for the seal element 20.

FIG. 2 illustrates in side sectional view, one example of the tubinghanger 10 being inserted within a tubing head 40 for assembly of awellhead assembly (FIG. 4). In this example, the outer radial surface ofthe tubing hanger 10 is shown sliding into a bowl 42 formed in thetubing head 40. A shoulder 44 is defined at a lower end of the bowl 42where the inner surface 46 of the bowl 42 extends radially inwardtowards axis A_(X). Above the shoulder 44 is a taper 48 that is definedwhere the inner surface 46 depends radially inward for an axialdistance. As shown, as the tubing hanger 10 is being inserted within thetubing head 40 the beads 28 on the outer leg 24 are set radially inwardfrom the inner surface 46 as long as the beads 28 are at a locationabove the taper 48.

As shown in FIG. 3, the tubing hanger 10 has landed within the tubinghead 40 and the lower lateral edge of the nut 36 is being supported onthe shoulder 44. Further, the respective locations of the taper 48 andridges 28 are strategically disposed so that when tubing hanger 10 is inthe landed position of FIG. 3, the ridges 28 are at a depth where theinner surface 46 is set radially inward so that the beads 28 are incompressive contact against the inner surface 46. As such, a sealingsurface is formed between the seal element 20 and inner surface 46, thesealing surface against the tubing head 40, in combination with asealing surface between beads 28 and groove 30 defines a sealing barrierbetween the tubing hanger 10 and tubing head 40. Further, the gap 25(FIG. 1) has disappeared due to the radial inward movement of leg 24against the lower member 18. In this instance, the lower member 18provides support for legs 24.

A side partial sectional view of an example of a wellhead assembly 50having the packoff assembly 12 is illustrated in FIG. 4. In thisexample, the wellhead assembly 50 is made up of a production tree 50 setabove the tubing head 40 and over a bore hole 54. In the example of FIG.4, the bore hole 54 extends through subterranean formation 56. Furtherincluded with the wellhead assembly 50 is a string of tubing 58 shownmounted on a lower end of tubing hanger 10 and projecting into the borehole 54.

Optionally, a soft metal, such as silver, may be set over the sealelement 20 provide a lubricating coating for when the tubing hanger 10is being landed within the tubing head 40. One example of operation, thepackoff assembly 12 (FIG. 1) is formed onto the tubing hanger 10 byfirst sliding the energizing ring 14 into upper groove 30 and thenadding the annular seal element 20 into upper groove 30 so that thelower member 18 extends between the legs 24 for providing support forthe legs 24. In one example, the outer leg 24 of the seal element issized to have an outer circumference just less than the innercircumference of the radius of the inner surface 46 so that duringlanding, up until the seal element 20 contacts the taper 48, the sealelement 20 is spaced radially inward from the inner surface 46. Reducingthe amount of sliding contact between the seal element 20 and innersurface 46 reduces chances of damage before the tubing hanger 10 islanded within the tubing head 40. After installing the seal element 20,the retainer nut 36 is screwed into place thereby locking the packoffassembly 12 to the tubing hanger 10. Again, as the tubing hanger 10 isbeing landed within the tubing head 40 the strategic location of thetaper 40 then engages the seal element 20 to create the seal between thetubing hanger 10 and tubing head 40. Although the energizing ring 14 maylift slightly during engagement of the seal element 20 with innersurface 46, the energizing ring 14 provides a backup force for legs 22and prevent legs 24 from collapsing. Optionally, outer diameter of theseal element 24 is electively changed to fit a particular size of thebowl 42. Moreover, in one example, the seal element 24 includes aflexible material, such as metal, so that when landing in tubing headshaving asymmetric bowls 42, the elasticity and flexibility of the sealelement 24 can from a full seal around the entire circumference of theinterface between the tubing hanger 10 and tubing head 40. An example ofusing a seal element 24 made from a metallic material over that of anelastomer is the ability to be deployed in lower depth but highertemperature wells.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present invention disclosed hereinand the scope of the appended claims.

What is claimed is:
 1. A wellhead assembly comprising: an outer tubularhaving a bore that defines a bore wall; an inner tubular insertable intothe bore and selectively set in a landed position in the bore; a packoffon the inner tubular; a taper strategically located in the bore, so thatwhen the inner tubular is inserted into the bore, the packoff is insealing contact with the bore wall when the inner tubular is proximatethe landed position, and the packoff is set radially inward from thebore wall when the inner tubular is above a location proximate thelanded position.
 2. The wellhead assembly of claim 1, wherein thepackoff comprises an energizing ring with a protrusion, a seal elementhaving spaced apart legs that terminate on opposing sides of theprotrusion, and a retaining nut threaded to the inner tubular and on aside of the seal element distal from the energizing ring.
 3. Thewellhead assembly of claim 2, wherein the seal element is a generallyannular member.
 4. The wellhead assembly of claim 3, wherein one of thelegs is spaced radially outward from the protrusion when the when theinner tubular is above a location proximate the landed position, andwherein the one of the legs is wedged between the taper and theprotrusion when the when the inner tubular is proximate the landedposition.
 5. The wellhead assembly of claim 2, wherein one of the legsprojects radially outward to define a seal between the outer tubular andthe seal element and wherein another one of the legs projects radiallyinward to define a seal between the inner tubular and seal element. 6.The wellhead assembly of claim 1, wherein the inner tubular is a tubinghanger and wherein the outer tubular is a tubing head.
 7. The wellheadassembly of claim 1, wherein the bore wall projects radially inward atan axial location below the taper to define a shoulder on which theinner tubular lands.
 8. A wellhead assembly comprising: an outer tubularhaving an axial bore; a taper formed in the bore where a surface of thebore projects radially inward; a shoulder formed in the bore below thetaper; an inner tubular landed on the shoulder; and a packoff having, anouter radius in sealing contact with the taper and set radially inwardfrom a portion of the bore between the taper and an upper end of thebore, and an inner radius in sealing contact with the inner tubular. 9.The wellhead assembly of claim 8, wherein the packoff comprises anenergizing ring, a seal element with legs spaced apart by the energizingring, and a retaining nut for urging the seal element against theenergizing ring, and beads on the legs that form a seal against theinner and outer tubulars.
 10. The wellhead assembly of claim 9, whereinthe seal element comprises metal.
 11. The wellhead assembly of claim 9,wherein the energizing ring comprises a protrusion on which the legs aresupported.
 12. The wellhead assembly of claim 8, wherein the innertubular comprises a tubing hanger and the outer tubular comprises atubing head.
 13. A method of sealing between tubulars in a wellheadassembly comprising: providing an inner tubular having a packoffcircumscribing a portion of the inner tubular; providing an outertubular having a bore with a taper so that a portion of the bore abovethe taper has a radius greater than a radius of the packoff, and aportion of the bore below the taper has a radius less than the packoff;and sealing between the packoff and the bore by inserting the innertubular into the outer tubular at least to a depth that the packoffcontacts the portion of the bore having a radius less than the packoff.14. The method of claim 13, further comprising landing the inner tubularin the outer tubular.
 15. The method of claim 13, wherein the packoffcomprises an energizing ring with a protrusion, a seal element havingspaced apart legs that terminate on opposing sides of the protrusion, asoft metal coating on the seal element, and a retaining nut threaded tothe inner tubular and on a side of the seal element distal from theenergizing ring.